Remove two timing gaps from the memory tests

Remove two timing gaps from the memory tests

The build limit test opens the gate of the fake summarizer only after
all 8 builds run, so its peak count no longer depends on goroutine
timing. The synthetic log test measures each view as the append did,
with the newest line as the pending mark, because the leaf of the new
message can be built before the check reads the view.

Issue: beb9a70